1. Field of the Invention
The present invention relates to a charging system for a vehicle for charging batteries carried on the vehicle.
2. Description of the Related Art
Recently, there is known a vehicle which carries two kinds of batteries with different voltages, that is, a main battery (for example, a 42V battery) and an auxiliary battery (for example, a 12V battery). In other words, there is known a vehicle which is capable of using properly two kinds of batteries with different voltages in such a manner the main battery is used to drive a motor requiring large electric power and the auxiliary battery is used to drive other units such as a control unit than the motor.
Now, FIG. 13 is a block diagram of a first example of a conventional charging system for charging the batteries of the above-mentioned type carried on a vehicle. This conventional charging system example includes two systems of charging circuits in order to charge two kinds of batteries with different voltages. That is, to charge a main battery 101, an alternating current generated by a motor generator 102 may be converted into a direct current by an inverter 104 which is controlled by a controller 103, and the thus-converted direct current may be supplied to the main battery 101. On the other hand, to charge an auxiliary battery 105, when an alternator 107 is rotated by an engine 106, a direct current generated by the alternator 107 may be supplied to the auxiliary battery 105.
Now, FIG. 14 is a block diagram of a second example of a conventional charging system for charging the batteries for vehicle of the above-mentioned type. In this example, there are used a DC/DC converter 108 changing the voltage in order to charge two kinds of batteries which differ in voltage from each other. That is, to charge a main battery 101, similarly to the first example, an alternating current generated by a motor generator 102 may be converted into a direct current by an inverter 104 which is controlled by a controller 103, and the-thus converted direct current may be supplied to the main battery 101. On the other hand, an auxiliary battery 105 can be charged by converting the output voltage of an inverter 104 using the DC/DC converter 108.
However, since the above-mentioned conventional charging systems require the alternator and DC/DC converter, the charging systems are complicated in structure and expensive in the manufacturing costs thereof.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional charging systems. Accordingly, it is an object of the invention to provide a charging system for a vehicle which is neither complicated in structure nor expensive in cost.
In attaining the above object, according to the present invention, there is provided a charging system for a vehicle, including: a motor generator which operates as a generator to generate an alternating current when the motor generator is driven by an internal combustion engine, and operates as a motor when an alternating current is supplied thereto; a switching circuit for converting an alternating current generated by the motor generator into a direct current; a first accumulator for accumulating therein the direct current converted by the switching circuit; a second accumulator for accumulating therein the direct current converted by the switching circuit and having an accumulation voltage smaller than that of the first accumulator; a first opening/closing unit interposed between the first accumulator and switching circuit; a second opening/closing unit interposed between the second accumulator and switching circuit; and, a control unit for controlling the opening and closing of the first and second opening/closing units.